Almost all bioassays make use of bioreagents (such as enzymes and small-molecule substrates) that are labile to various degrees and require special shipping and storage. The instability of these molecules can arise from either thermal denaturation or chemical modification, such as oxidation or hydrolysis. Because of these issues, they often have to be shipped on dry ice with special packaging, which is costly. These reagents also have to be stored in bulk in refrigerators or freezers to minimize loss of activity, but they must be retrieved, thawed, and aliquoted for intended tests that are often performed at room temperature. Repeated freezing and thawing can result in significant loss of activity, which often leads to less reliable test results.
Pullulan is a natural polysaccharide produced by the fungus Aureobasidium pullulans.1 It readily dissolves in water but resolidifies into films upon drying.1a,1b,2 The film forming property of pullulan has been utilized in some unique applications in the pharmaceutical and food industries, such as breath fresheners and food additives.1b,3 Recent studies have found that pullulan coatings applied to food packaging can act as oxygen barriers to prolong the shelf life of various foods.2,4 In addition, pullulan has been shown to preserve the viability of bacteria under various storage conditions.3 
U.S. Pat. No. 7,604,807 describes the reversible preservation of biological samples in compositions comprising natural polymers such as pullullan or acacia gum.